This inventiion relates to a method for improving the stability of diesel fuel compositions by adding to diesel fuel compositions certain rare earth-organic compounds.
Diesel fuel compositions are known to be very unstable. The expression "diesel fuel" is employed in the description and claims to designate the hydrocarbon fraction which distills from kerosene. Generally, diesel fuel comprises a mixture of hydrocarbons boiling in the range from about 350.degree. to about 700.degree. F. The property requirements of diesel fuel given in Federal Specification VV-F-800 as of 1967 are given in the approximate ranges set forth below. Diesel fuels are graded as DF-A (arctic), DF-1 (winter), DF-2 (regular) and DF-4 (heavy). Arctic grade is used in high-speed, automotive-type diesel engines and pot-type burner space heaters in environments having ambient temperatures below -25.degree. F. Winter-grade is used in high-speed automotive service where temperatures are as low as -25.degree. F. Regular grade diesel fuel is used in automotive, high-speed engines and in medium-speed stationary engines where ambient temperatures are above 20.degree. F. Heavy grade diesel fuel is used in low and medium-speed engines.
The properties of such fuels include flash points ranging from 100.degree. F. (arctic) to 130.degree. F. (heavy); a cloud point of -50.degree. F.; a pour point of -70.degree. F.; a kinematic viscosity (at 100.degree. F.) ranging from a minimum of 1.4-5.8 centistokes to a maximum of 4.0-20.6 centistokes; a limit as to water and sediment content (volume percent) from 0.03 to 0.50%; sulfur content from 0.25 to 1.5% carbon residue (an 10% residuum) of 0.12 to 05% maximum; ash content, 0.01 to 0.10 percent maximum; corrosion (measured by copper strip, 3 hr. at 122.degree. F., ASTM number, max.) of 2-3; and ignition quality (cetane number, minimum) of 35 to 40. Further information concerning diesel fuels may be found in Bland, et al., Editors, "Petroleum Processing Handbook" (McGraw-Hill Book Co., 1967), pp. 11-35 et seq., hereby incorporated herein be reference.
Diesel fuel contains a great number of constituents. In addition to the oil fractions used as fuel, many chemical components are included fuel for several purposes. These chemical additives are used e.g., for oxidation inhibition to prevent sludge formation, corrosion prevention, for detergent and dispersant action, for emulsification, metal deactivation, antistatic action and as biocides.
An important problem in formulating diesel fuel is that some of the components, unsaturated hydrocarbons for instance, tend to react and precipitate out of the composition during storage, causing various concerns including fouling of tanks and engines. Further, some of the additives become selectively combined with the precipitate and are no longer present in the diesel fuel composition and, hence, cannot perform their intended functions.
One of the most important classes of diesel fuel additives is that of oxidation inhibitors. Because diesel fuel is a mixture of hydrocarbons, it is highly susceptible to free radical oxidation and formation of acids, ketones, aldehydes and esters. Oxidation forms gums which become colloidal, agglomerate and precipitate as sludge. Sludge can plug oil lines, strainers and burner nozzles.
Many oxidation inhibitors function by removing the peroxy radicals from the reaction chain, thus stopping the reaction. Phenol-type oxidation inhibitors such as 2,4-dimethyl-6-tert-butyl phenol and 2,6-di-tert-butyl-4-methyl phenol function in this manner. Other oxidation inhibitors include amines such as N,N'-di-sec-butyl p-phenylene diamine and amine borates, phosphorus- and sulfur-containing compounds such as esters of dithiophosphoric acid, barium and zinc salts of these acids and glycerol acids containing metal oxides.
Another important class of diesel fuel additives is that of metal deactivators. These compounds generally act to chelate the metals found in diesel fuels by surrounding and isolating metals in complexes that remain soluble in the fuel instead of precipitating.
Various other additives have been suggested for use in diesel fuels to reduce particulate emissions. U.S. Pat. Nos. 3,410,670; 3,413,102; 3,539,312 and 3,499,742 are representative ones which describe smoke suppressants that can be employed in diesel fuels. U.S. Pat. No. 4,207,078 sets forth a method for reducing soot and visible particulate matters from the exhaust of diesel fueled engines by incorporating in the diesel fuel an additive consisting of a mixture of an oxygenated compound and an alkylcyclopentadienyl manganese tricarbonyl.
U.S. Pat. No. 4,222,746 describes another group of compounds for reducing soot and visible particulates emitted from the exhaust of diesel fueled internal combustion engines. According to this patent, the addition of wax to diesel fuel which oxidizes along with a fuel soluble organometallic compound such as alkyl cyclopentadienyl manganese tricarbonyl complex salts can reduce emissions of soot and visible particulates.
Due to environmental, regulatory and economic concerns, combustion promoters have been developed to improve the efficiency of the combustion of the hydrocarbons in diesel fuel. During the operation of a diesel-fueled engine, the combustion promoter serve to encourage the burning of the hydrocarbons.
According to U.S. Pat. No. 4,522,631, certain soluble rare earth octoate compounds of the formula: ##STR1## have been added to diesel fuel as combustion promoters. Cerium octoates were found to be particularly effective. However, cerium octoates tend to contribute to the formation of precipitate and sludge in diesel fuels.
An objective of this invention is to provide compounds for stabilizing diesel fuel so as to substantially prevent diesel engine fouling by reducing the accumulation of sludge in diesel fuel.
Another objective of this invention is to provide a method of reducing precipitation of particulates in diesel fuel during storage periods over relatively long periods of time.
Another objective of this invention is to provide a method of maintaining the various additives of diesel fuel in solution during storage so as to allow them to perform their functions during storage and combustion.
Yet another objective of this invention is to provide a method for substantially reducing precipitation in diesel fuels using certain rare earth compounds.